Conventionally, a vehicle that runs by drive power from at least one of an engine or a motor, i.e., a so-called hybrid vehicle, is known. The hybrid vehicle selectively uses the engine and the motor in accordance with the running state of the vehicle and the like, so as to make full use of their respective characteristics. One suggested hybrid vehicle allows a driver to select an EV running mode for stopping the engine and running the vehicle by the motor supplied with electric power from a battery. The engine is stopped and the vehicle does not produce any exhaust gases or noises of the engine during the EV running mode, and therefore it is particularly suitable for driving in a residential area late in the night or early in the morning.
Japanese Patent Laying-Open No. 11-75302 discloses a hybrid vehicle that can run also as an electric vehicle without operating an engine. The hybrid vehicle described in Japanese Patent Laying-Open No. 11-75302 includes: an internal combustion engine; a first electric generator directly coupled to the rotation shaft of the internal combustion engine; a transmission provided on the output side of the first electric generator through a first clutch; a transmission drive selectively setting the gear ratio of the transmission in accordance with an electric signal; a power connection gear coupled between the first clutch and the transmission; a second electric generator coupled to the power connection gear through a second clutch; a clutch drive jointing/disjointing the second clutch in accordance with an electric signal; an EV mode control unit performing acceleration or braking by the second electric generator with the first clutch disjointed; and a transmission control circuit electrically coupled to the EV mode control unit and providing a controlling electric signal to the transmission drive and the clutch drive in accordance with driving operation information.
The hybrid vehicle, when the charging amount of the charging cell reaches a predetermined value, prohibits the EV mode and starts the engine to rotate the first electric generator, whereby the first electric generator is driven as a generator to charge the charging cell. Here, the second electric generator is supplied with electric power from the charging cell, whereby the second electric generator is driven as an electric motor to run the vehicle.
When the charging amount of the charging cell becomes smaller than a predetermined value, the first and second electric generators are stopped and the engine is started, to run the vehicle by the drive power of the engine.
According to the hybrid vehicle described in the publication, in a hybrid vehicle that can be driven as an electric vehicle coupling the power connection gear, coupled between the transmission and the first clutch, and the second electric generator through the second clutch while not operating the internal combustion engine, control of the second clutch and the transmission can also be attained properly and automatically, and the speed can be changed by the transmission.
Japanese Patent Laying-Open No. 2003-23703 discloses a control apparatus of a hybrid vehicle that charges a battery just by the required amount when EV mode is requested to ensure driving in the EV mode. The control apparatus described in Japanese Patent Laying-Open No. 2003-23703 includes: a circuit to which a hybrid running mode, for running the vehicle by driving an electric motor while driving a generator by an engine, and an EV running mode, for running the vehicle by driving the motor only by electric power from a battery without driving the engine, are set; a mode switching circuit switching these running modes; an input circuit specifying the driving range by the EV running mode; a charging control circuit charging the battery to a charging amount required for driving in the EV running mode through the input EV running range; and a circuit enabling switching to the EV running mode when the battery is charged to a required amount.
According to the control apparatus of the hybrid vehicle described in the publication, when an EV running range is specified, the battery is charged just by the amount required for driving in the EV running mode through the running range. Therefore, the battery power will not fail or charged excessively during driving in the EV running mode. Thus, the battery is not increased in size and the EV running can surely be achieved.
As the engine is driven by combustion of fuel, the hybrid vehicle likewise emits exhaust gases, which necessitates a catalyst for purifying the exhaust gases. Additionally, the catalyst must be warmed up sufficiently in order to exert exhaust gas purifying effect. It is known that warming up to raise the temperature of the catalyst is necessary, for example, when starting up the engine that has been stopped for a long period.
However, the hybrid vehicle described in Japanese Patent Laying-Open No. 11-75302, when the charging amount of the charging cell reaches a predetermined value, prohibits the EV mode and starts the engine to rotate the first electric generator, whereby the first electric generator is driven as a generator to charge the charging cell. Here, the second electric generator is supplied with the stored electric power, whereby the second electric generator is driven as an electric motor to run the vehicle. Accordingly, the engine must be driven with the output that allows the second electric generator to be driven and electric power required for charging the charging cell to be generated, even during warming-up of the catalyst.
When the charging amount of the charging cell becomes smaller than the predetermined value, the first and second electric generators are stopped and the engine is started, to run the vehicle by the drive power of the engine. Accordingly, the engine must be driven with the output required for driving the vehicle, even during warming up of the catalyst.
In either case, exhaust gases may be emitted in an amount exceeding the purifying capability of the warming-up catalyst.
The hybrid vehicle described in Japanese Patent Laying-Open No. 2003-23703 permits the EV running only when the charging amount of the battery satisfies the charging amount required for driving in the EV running mode through the running range. Accordingly, when the catalyst is not warmed up, for example, after stopped for a long period, and the charging amount of the battery is not in the charging amount required for driving in the EV running mode through the running range, the EV running cannot be performed and it is necessary to start the engine for running the vehicle by the drive power of the engine. Accordingly, the engine must be driven with the output necessary for running the vehicle, even during warming up of the catalyst. Thus, exhaust gases may disadvantageously be emitted in an amount exceeding the purifying capability of the warming-up catalyst.